Projectile for a mortar having a nonrifled bore



1964 J. R. JASSE 3,143,074

PROJECTILE FOR A MORTAR HAVING A NON-RIFLED BORE 7 Filed June 28, 1961 2 Sheets-Sheet 1 Aug-4,1964 J. R. JASSE 3,143,074

- PROJECTILE FOR A MORTAR HAVING A NONRIFLED BORE I Filed June 28, 196i 12 She'efcs-Sheef 2 United States Patent 3,143,074 PRUJECTILE FGR A MGRTAZR HAVING A NfiN- RELED BORE Joseph Raymond .lasse, Paris, France, assignor to Hotel:- kiss-Brandt, Paris, France, a corporation of France Filed June 28, 1961, Ser. No. 120,429 Claims priority, application France June 29, 196i) 5 (Ilm ms. (Cl. 102-92.5)

The present invention relates to projectiles for mortars, which have a non-rifled bore and are loaded through the muzzle and more particularly to finned projectiles.

It is known that when the loading is effected through the muzzle, in order to ensure that the velocity of the drop of the projectile through the gun tube be high enough to result, in the case of an automatic percussion, in an effective percussion when the cartridge of the projectile comes into con-tact with the point of the striker which protrudes from the inner face of the breech block of the mortar, it is necessary to provide a certain clearance between the outer face of the projectile and the smooth inner face of the gun tube. However, upon firing, this clearance results in an escape of the gas emanating from the powder of the cartridge and this diminishes the initial velocity of the projectile and markedly increases the possible variations in this velocity because the escape of gas varies with this clearance.

In order to overcome this drawback, which considerably impairs firing precision, it has already been proposed to provide projectiles for non-rifled muzzle-loaded mortars with a belt or ring of metal or plastic material disposed in a groove formed in the outer face of the body of the projectile in the region of the latter which is guided in the gun tube, this groove having a sectional size in a radial axial plane of the projectile which is longer than the diameter of the section of the ring and comprising a sloping bottom face along which the ring travels from a position of rest or loading, in which the ring provides relative to the inner face of the gun tube a clearance facilitating the descent of the projectile in the gun tube, to an operative position to which the belt is automatically brought by the thrust of the projectilelaunching gases and in which the ring is enlarged and bears against the inner face of the gun tube and this provides a fluid-tight seal between the projectile and the gun tube.

Howeventhe shapes proposed heretofore for the groove do not fully solve the considered problem. Indeed, with the known shapes, the slope along which the ring travels in the groove under the effect of the pressure of the gases produced by the projectile launching powder so as to come into contact with the inner face of the gun tube, makes with the longitudinal axis of the projectile, and consequently with said inner face, a large angle varying between 35 and 60. In consequence, the displacement of the ring from the position of rest to the operative position requires a relatively high thrust, and under these conditions it sometimes occurs that the sealing ring fails to provide a suitable seal, above all when the launching thrust or force is small and does not result in a sufficient displacement of the ring along the groove.

Furthermore, this ring must become detached from the projectile when the latter leaves the motar but it sometimes remains on the body of the projectile or even travels along the latter and becomes hooked on the projectile fins which in either case exerts a drag on the projectile on its trajectory and results in the projectile falling short of the target and may also considerably increase the dispersion in direction.

The object of the invention is to provide a projectile of the aforementioned known type having a sealing ring of plastic material disposed in a groove in the body of 3,143,974 Patented Aug. 4,1964

the projectile, the latter being improved so as to overcome the aforementioned drawbacks.

This is obtained due to the fact that the slope of the bottom face of the groove is less than 25 and preferably about 10. Preferably, this groove is arranged to have a conical bottom having the aforementioned slope and two rounded end faces or fillets.

Further features and advantages of the invention will be apparent from the ensuing description, with reference to the accompanying drawings to which the invention is in no way limited.

In the drawings:

FiG. 1 is a diagrammatic longitudinal. and diametral sectional view of a projectile according to the invention;

FIG. 2 is a partial longitudinal sectional view on an enlarged scale of the guide and sealing portion of the projectile and of the adjacent gun tube;

PEG. 3 is a front elevational view of the sealing ring in the free state;

FIG. 4 is a front elevational view of another embodiment of the sealing ring for the projectile according to the invention, and

FIG. 5 is a partial view of the ring shown in FIG. 4 on an enlarged scale.

in the illustrated embodiment, the invention is applied to a projectile P whose body 1 of conventional shape is provided at its forward end with a screw-threaded aperture 2 for receiving a fuze and at its rear end with a wall 3 having on its outer face a blind hole 4 provided for the attachment of a projectile fin arrangement (not shown in the drawings).

The body 1 comprises on its outer face 5 a portion ab which corresponds to the maximum diameter of the body and is, for example, cylindrical and is provided for the guiding of the projectile against the smooth inner face S of the gun tube T.

According to the invention, there is provided just at the rear of the portion ab in the face 5 a transverse groove 6 containing a ring 7 of plastic material.

The longitudinal section bc of the groove 6 in a radial axial plane intersecting the longitudinal axis X--X of the projectile comprises:

A forward fillet having a part-circular section be, a centre 0 and a radius r;

A bottom face having a rectilinear section ad which is rearwardly convergent relative to the longitudinal axis X--X of the projectile, this face therefore constituting a conical face whose half angle x at the apex is less than 25 and is preferably about 10;

A rear part-circular fillet de composed approximately of a quarter of a circle and having a radius r equal to that of the forward fillet, its centre 0 being located at a distance from the axis X-X of the projectile which is roughly equal to that of the corner or edge e constituting the rear end of the groove 6.

The elastic ring '7 is composed of a plastic material. For this there could be used, for example, the material known under the trade name Rilsan which is a superpolyamide produced by the French Company Organico or the material known under the trade name Nylon and in a general way the various polyamides and superpolyamides, their copolymers, the polyethylenes and any other substances having similar physical properties.

The ring 7 has in its free state 7 (FIG. 3) a circular circumference less than that of the groove 6 at the deepest point d of the latter and a cross-sectional shape having a radius r so that when this ring is disposed in the groove it is put under peripheral stress and its cross-section has a radius approximately equal to the radius r of the fillets of the groove.

Now, if: I

D is the diameter of the smooth inner face S of the gun tube T;

D is the diameter of the cylindrical portion ab corresponding to the calibre of the projectile P;

D is the diameter corresponding to the deepest point d of the groove;

D is the diameter corresponding to the point e of the rear end of the groove;

And bearing in mind the radial cross-section of the ring 7 in the free state: These diameters and this section are such that the projectile P provides inside the tube T a small clearance j equal to Dy-Dg 2 in the guiding portion ah;

The centre of the section of the ring 7 under stress at d in the bottom of the groove coincides at with the centre of the section de of the rear fillet of the groove;

The ring provides in this position relative to the face S a clearance substantially equal to the clearance i.

It will be observed that in its free state (FIG. 3) the ring includes a number of rupture-initiating notches 8 provided on the outer and/or inner face of the ring.

The number of these notches is not critical, there being provided preferably three or four notches.

The projectile according to the invention operates in the following manner:

Before dropping it into the mortar, the projectile P is provided with the sealing ring which is disposed at 7 at the rear end of the groove 6 in the position shown in full line in FIGS. 1 and 2. Under these conditions, the pro= jectile can be dropped through the muzzle end of the gun tube, the latter being downwardly inclined in the direction from the muzzle to the breech.

The clearances e provided between the smooth bore S of the gun tube T and, on the one hand, the portion ab of the projectile and, on the other hand, the ring 7, perinit at substantially free and rapid fall of the projectile through the tube so that in the case of an automatic firing the cartridge of the projectile comes rapidly into contact with the striker at the end of its downward travel at such velocity as to ensure percussion.

As the outer face of the projectile at e at the rear end of the groove 6 has a diameter D; which approximately coincides with the mean diameter of the ring, the latter offers substantially half of its surface to the thrust of the launching gases, this surface corresponding to the portion thereof protruding from the groove. Thus the ring is driven forward by the action of this thrust. Upon firing, the ring is therefore driven forwardly relative to the body 1 of the projectile and rides up the slope dc of the groove 6. Very rapidly the clearance j between the ring 7 and the face S is taken up and then this ring is progressively elastically deformed. Thus it provides a good seal between the face S of the gun tube T and the projectile in the course of the travel of the latter through this tube. Owing to the small angle x of the bottom face 6 of the groove, the foregoing occurs even when the launching charge is small, that is, when the ring is subjected to a relatively small forward thrust.

In any case, whether the charge be large or small, owing to the slight slope of the bottom of the groove there is obtained a high specific pressure between the ring 7 and the inner face S of the tube T and this produces a relatively high wear of the ring or plastic material while the projectile is being driven out of the gun tube. Owing to this high wear and moreover owing to the presence of the rupture-initiating notches 8, the ring under stress in the forward part of the groove 6 breaks and its broken portions fall away from the projectile.

Thus there is no risk of the ring remaining on the projectile and in particular becoming attached to the rear fin arrangement which would create an additional drag and result in the projectile falling short of the target.

FIGS. 4 and 5 show another embodiment of the sealing ring 7 which is in the form of a tore and has a cir cular cross-sectional shape and a number of large recesses 8 and 3 disposed facing each other in pairs. In the presently-described embodiment, four pairs of recesses are provided, the pairs being at to each other.

These recesses have a concave bottom and, when viewed in side elevation, a part-circular or an approximately partcircular shape. Being placed facing each other in pairs, these recesses sufliciently reduce at y the radial thickness of the ring to facilitate the rupture of the latter as soon as the projectile leaves the gun tube without rendering the ring fragile in the course of handling.

For example, in respect of a ring composed of said plastic material Rilsan" having an inside diameter D (FIG. 1) equal to 75 mm. and a radius r (FIG. 5) of its cross section equal to about 1.25 mm., y could be about 0.8 mm. and R (radius of the recesses 8 could be about 8.1 mm.

Although specific embodiments of the invention have been described, many modifications and changes may be made therein without departing from the scope of the invention as defined in the appended claims.

Having now described my invention what I claim as new and desire to secure by Letters Patent is:

1. In a projectile adapted to be fired by a launching charge from a launching gun tube and provided with a sealing ring of expandable material and having an outside diameter smaller than the inside diameter of the launching tube and combined with an annular recess in the projectile for sealing radial clearance between the projectile and the launching tube, the ring being ordinarily located at the rear end of the recess and the recess having a forwardly divergent annular face which closely engages the ring so as to expand the ring as the ring is urged forwardly relative to the projectile by the launching charge, the provision of small recesses on a periphery of the ring, said recesses forming throughway passages between the ring and one of two elements consisting of the launching tube and the divergent face, whereby when the projectile is launched the hot gases of the launching charge urge the ring forwardly in sealing engagement with the launching tube and the destructive effect of a small proportion of said gases passing through said passages reduces the tensile strength of the ring in the region of the recesses so that the ring ruptures as the projectile issues from the launching tube.

2. In a projectile adapted to be fired by a launching charge from a launching gun tube and provided with a sealing ring of expandable material and having an outside diameter smaller than the inside diameter of the launching tube and combined with an annular recess in the projectile for sealing radial clearance between the projectile and the launching tube, the ring being ordinarily located at the rear end of the recess and the recess having a forwardly divergent annular face which closely engages the ring so as to expand the ring as the ring is urged forwardly relative to the projectile by the launching charge, the provision of small recesses on the inner and outer peripheries of the ring, said recesses forming pairs of throughway passages in different radial planes of the projectile between the ring and the launching tube and the divergent face, whereby when the projectile is launched the hot gases of the launching charge urge the ring forwardly in sealing engagement with the launching tube and the destructive effect of a small proportion of said gases passing through said passages reduces the tensile strength of the ring in the region of the recesses so that the ring ruptures as the projectile issues from the launching tube.

3. In a projectile adapted to be fired by a launching charge from a launching gun tube and provided with a sealing ring of expanded material and having an outside diameter smaller than the inside diameter of the launching tube and combined with an annular recess in the projectile for sealing radial clearance between the projectile and the launching tube, the ring being ordinarily located at the rear end of the recess and under circumferential tension at said rear end, the combination of small recesses on a periphery of the ring, said recesses forming throughway passages between the ring and one of two elements consisting of the launching tube and the divergent face, and a cross-sectional shape of the ring in radial planes of the projectile which has a curved contour providing a point contact between the ring and the launching tube and between the ring and the divergent face in said radial planes, whereby when the projectile is launched the hot gases of the launching charge urge the ring forwardly in sealing engagement with the launching tube and the destructive effect of a small proportion of said gases passing through said passages combined with an outward radial component of the thrust of said gases acting on the curved cross-sectional shape of the ring cause rupture of the ring as the projectile issues from the launching tube.

4. In a projectile adapted to be fired by a launching charge from a launching gun tube and provided with a sealing ring of expandable synthetic plastics material and having an outside diameter smaller than the inside diameter of the launching tube and combined with an annular recess in the projectile for sealing radial clearance between the projectile and the launching tube, the ring being ordinarily located at the rear end of the recess and the recess having a forwardly divergent annular face which closely engages the ring so as to expand the ring as the ring is urged forwardly relative to the projectile by the launching charge, the combination of small recesses on a periphery of the ring, said recesses forming throughway passages between the ring and one of two elements consisting of the launching tube and the divergent face and a round cross-sectional shape of the ring in radial planes of the projectile, whereby when the projectile is launched the hot gases of the launching charge urge the ring forwardly in sealing engagement with the launching tube and the destructive elfect of a small proportion of said gases passing through said passages combined with an outward radial component of the thrust of said gases acting on the round cross-sectional shape of the ring cause rupture of the ring as the projectile issues from the launching tube.

5. In a projectile adapted to be fired by a launching charge from a launching gun tube and provided with a round-sectional sealing ring of expandable synthetic plastics material and having an outside diameter smaller than the inside diameter of the launching tube and combined with an annular recess in the projectile for sealing radial clearance between the projectile and the launching tube, the ring being ordinarily located at the rear end of the recess and the recess having a forwardly divergent annular face which closely engages the ring so as to expand the ring as the ring is urged forwardly relative to the projectile by the launching charge, the provision of small recesses on the inner and outer peripheries of the ring, said recesses forming pairs of throughway passages in diiferent radial planes of the projectile between the ring and the launching tube and the divergent: face, the radius of the round section of the ring being about 1.5 times the radial thickness of the ring between each pair of recesses, each of said recesses having in the plane of the ring an arcuate face whose radius is about 10 times said radial thickness, whereby when the projectile is launched the hot gases of the launching charge urge the ring forwardly in sealing engagement with the launching tube and the destructive effect of a small proportion of said gases passing through said passages reduces the tensile strength of the ring in the region of the recesses so that the ring ruptures as the projectile issues from the launching tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,325,560 Wauters July 27, 1943 2,616,372 Frantik Nov. 4, 1952 3,023,704 Dawson et all Mar. 6, 1962 FOREIGN PATENTS 507,107 Great Britain June 9, 1939 

1. IN A PROJECTILE ADAPTED TO BE FIRED BY A LAUNCHING CHARGE FROM A LAUNCHING GUN TUBE AND PROVIDED WITH A SEALING RING OF EXPANDABLE MATERIAL AND HAVING AN OUTSIDE DIAMETER SMALLER THAN THE INSIDE DIAMETER OF THE LAUNCHING TUBE AND COMBINED WITH AN ANNULAR RECESS IN THE PROJECTILE FOR SEALING RADIAL CLEARANCE BETWEEN THE PROJECTILE AND THE LAUNCHING TUBE, THE RING BEING ORDINARILY LOCATED AT THE REAR END OF THE RECESS AND THE RECESS HAVING A FORWARDLY DIVERGENT ANNULAR FACE WHICH CLOSELY ENGAGES THE RING SO AS TO EXPAND THE RING AS THE RING IS URGED FORWARDLY RELATIVE TO THE PROJECTILE BY THE LAUNCHING CHARGE, THE PROVISION OF SMALL RECESSES ON A PERIPHERY OF THE RING, SAID RECESSES FORMING THROUGHWAY PASSAGES BETWEEN THE RING AND ONE OF TWO ELEMENTS CONSISTING OF THE LAUNCHING TUBE AND THE DIVERGENT FACE, WHEREBY WHEN THE PROJECTILE IS LAUNCHED THE HOT GASES OF THE LAUNCHING CHARGE URGE THE RING FORWARDLY IN SEALING ENGAGEMENT WITH THE LAUNCHING TUBE AND THE DESTRUCTIVE EFFECT OF A SMALL PROPORTION OF SAID GASES PASSING THROUGH SAID PASSAGES REDUCES THE TENSILE STRENGTH OF THE RING IN THE REGION OF THE RECESSES SO THAT THE RING RUPTURES AS THE PROJECTILE ISSUES FROM THE LAUNCHING TUBE. 